The belt-driven data tape cartridge of von Behren, U.S. Pat. No. 3,692,255 has become a standard interface with computers where rapid acceleration and deceleration of the tape are required. In these reel-to-reel tape cartridges, an elastic driving belt extends along a belt path around corner guide rollers positioned adjacent the tape reels, contacts the tape on the reels, and drives the tape from reel to reel. A tape path extends between the reels and along one edge of the cartridge across a cutaway portion providing access to the tape by a transducer such as a magnetic read/write head which is a part of a tape drive which receives the cartridge. The tape path is defined by a guide pin, a pair of tape guides, and in some cartridges, a pair of tape wrap pins. One tape wrap pin is positioned between each reel and the adjacent tape guide to deflect the tape from a straight line path between the tape supply on the reel and the tape guide. This increases the frictional coupling between the tape and the tape wrap pin as the amount of tape wound on the reel increases and helps to maintain constant tape tension at the magnetic head.
Belt driven tape cartridges must meet minimum tape tension specifications while simultaneously maintaining minimum drive force specifications. The tape tension must not fall below a certain level as the tape passes from reel to reel or contact between the read/write head and the tape will be insufficient. The minimum achievable tape tension should be sufficiently high to ensure proper cartridge operation. Similarly, the maximum required frictional drive force should be as low as possible to enhance cartridge operation within the power limitations of the drive motor. Thus, there is a limitation on the frictional drive force. The frictional drive force is that portion of the drive force which affects power loss at the interface between the tape backside and the tape guide. There is a continuing need to further minimize the frictional drive force and to improve tape tracking thereby to further enhance cartridge operation. This can be accomplished by minimizing the friction at the interface between the tape and the tape guides, which accounts for approximately one-third of the drive force in a data cartridge.
Early tape guides were made of a plurality of separate components staked together by a rivet. Upper and lower flanges or washers were fastened on the ends of a tape guide spacer. However, this system of assembly was subject to imprecise operation over time. The riveting did not adequately maintain the integrity of the assembly to a degree required by the current generation data tape cartridges.
Injection molded plastic parts, while mass producible, do not guarantee durability, nonshedding, holding tight tolerances, or maintaining rigidity during use. Additionally, static build-up and dust collection are associated with dielectrics.
The current generation tape guides are made of a single piece of material that is machined, ground, or cast, from a solid mass, such as non-magnetic stainless steel. This single piece construction requires that the tape guide be machined to form accurately the distance between the flanges and the overall part. Using stainless steel as a material for precision tape guides has resulted in expensive parts, due to the limited number of methods available for working stainless steel.